In this connection the invention shall include disc brakes which either comprise a sliding caliper or a fixed caliper, and which overlap one or more brake discs. Mainly but not exclusively the invention relates to disc brakes with lining sections of the spot-type.
Disc brakes, in particular for heavy load trucks, with different configurations are known both with respect to the type of the brake actuation mechanism, with respect to the way of the transmission of the braking force onto one or several brake discs and with respect to the type of the adjustment for compensating the wear of the brake pads and brake linings, respectively.
For example, one specific embodiment of a brake actuation mechanism, which is embodied in disc brakes, is known from International Application WO 2011/113554 A2 of the applicant. The brake actuation mechanism as known from this application is characterized by a very compact structure, which is associated with reduced space requirements in the housing of the brake caliper and with a smaller weight. It is easy to mount and its single components can be made in an easy and cheap manner due to their, by the majority, rotational symmetric configuration.
The brake actuation mechanism for a disc brake as known from this publication having a brake caliper, preferably a sliding caliper, comprises an amplification mechanism for introducing a clamping force, an adjustment mechanism for compensating a wear of the brake pads, which includes a torque clutch, a thrust element for transmitting the clamping force onto the brake disc and a return mechanism, wherein the amplification mechanism, the adjustment mechanism, the thrust element and the return mechanism are mounted in the brake caliper in a functional interacting manner by means of a rod, which is supported in axial direction in the housing of the brake caliper, in such a way that these components act in parallel to the rotational axis of the brake disc.
For that purpose, the configuration and dimensioning of the rod is selected so that the single brake components either in different module units or the brake actuation mechanism in its entirety, each as self-supporting units, will be supported on the rod on the one hand and thereby in the housing of the brake caliper on the other and will be held in the rear section of the housing of the brake caliper which section faces away from the brake disc.
The thrust element for transmitting the clamping force onto the brake disc comprises an adjustment spindle which in turn is in threaded engagement with a thrust piece cooperating with a brake pad, wherein the thrust piece is axially guided in the housing of the brake caliper in a non-rotatable manner, so that a rotation of the adjustment spindle will result in an axial displacement of the thrust piece. The adjustment mechanism for compensating a clearance (or slack) comprises a torque clutch, which is controlled by torques and which serves for the selective transmission of a rotation between the elements of the torque clutch depending on the rotational direction.
Furthermore, the adjustment mechanism comprises a sprag (or wrap) spring serving as an one-way clutch, which connects two elements, an internal holding (or receiving) sleeve and a hollow shaft, being rotatably supported on the rod, wherein the sprag spring is enclosed coaxially on the rod by these both elements. For that purpose, the one-way clutch configured in such a way is designed, so that it transmits a rotational motion between these both elements during brake actuation, while it slips upon brake release, so that then no rotational movement will be transmitted between these elements. In that way, it is ensured that upon brake release no rotational movement of the elements occurs in the opposite rotational direction, which basically is undesired. Such a rotational movement would lead to a rearward travel motion of the adjustment mechanism, i.e. being directed away from the brake disc, which travel motion would result in an axial displacement of the thrust piece being directed away from the brake disc and would thus again increase the clearance to some extent, which clearance previously has been compensated during brake actuation upon advancement of the thrust piece by means of the adjustment mechanism.
With respect to the exact functioning as regards clamping and transmitting of the brake force as well as regards adjustment of the clearance of the brake actuation mechanism as known from the prior art, it should herewith expressively be referred to the disclosure of WO 2011/113554 A2.
Under certain circumstances a certain, however small risk exists with respect to the above-mentioned brake actuation mechanism, in that the adjustment mechanism and the thrust piece, respectively, could nevertheless move away from the brake disc, if no more brake force will be transmitted.
It can thus not always be guaranteed, that the sprag spring will always slip and decouple the internal holding sleeve from the hollow shaft upon release of the brake. It is possible that still a certain, but nominal small torque can appear in the slipping direction of the one-way clutch, which could effect a rotation of the elements in a direction opposite to the direction of the rotational transmission between the elements upon brake actuation, though by a few degrees only.
Under certain circumstances a further problem could exist in that single frictional contacts between the single components of the brake actuation mechanism as such and the resulting sum of all these frictional contacts, respectively, will be sufficient in order to cause a torque upon release of the brake, i.e. in case no more clamping force is transmitted through the brake actuation mechanism and through its single components and thus also through the adjustment mechanism, which torque will be large enough to apply a rotation onto components, which components shall not rotate upon release of the brake, wherein under certain circumstances this rotation as transmitted onto such components could effect a counter-rotation of the adjustment mechanism and thus a return motion of the thrust piece.
If for some reasons the frictional resistance, which exists in the threaded contact between the adjustment spindle and the thrust piece, is smaller than expected, the afore-mentioned risk of an unwanted return motion of the entire adjustment mechanism will increase, since normally this frictional resistance, possibly together with other frictional forces existing inside the entire brake actuation mechanism, is aimed to create some resistance against rotations in the latter or at least in single components of it, which resistance is sufficient so that the one-way clutch always enables slipping unresistingly.
Basically, it would be possible to reduce or entirely exclude the afore-mentioned risk, if the friction resistance will be increased directly in the threaded contact and threaded engagement, respectively, between the adjustment spindle and the thrust piece. This, however, could be only realized up to a certain extent, since at the same time thereby an unnecessary resistance will be applied to the rotational movement for compensating the clearance during brake actuation.
Moreover, it would be very difficult to determine and to control the desired frictional resistance of and inside an entire arrangement, which comprises several components, which are functionally interacting together by different means, such as for example the afore-mentioned brake actuation mechanism having an integrated adjustment mechanism according to the prior art, with sufficient accuracy, since amongst other things also manufacturing tolerances and other deviations resulting from manufacturing could take influence.
Thus, in total it can happen that a clearance, which has been previously adjusted by means of the adjustment mechanism, cannot be maintained during the subsequent release of the brake, which speaks against a sufficient functional safety and reliability of the adjustment mechanism.
From this disadvantage the aim results to almost reduce, or to even entirely exclude the afore-mentioned risk of an unwanted return motion in a brake actuation mechanism for a disc brake.
In this connection, the invention is preferably directed to a brake actuation mechanism, which as such is disclosed in WO 2011/113554 A2, to which disclosure it is herewith expressively referred; however, the invention is not limited to such a brake actuation mechanism. Rather, the invention can be also employed with brake actuation mechanisms, for which generally a risk of an unwanted reset motion exists by means of the adjustment mechanism during brake release, independent from its actual functional and constructional design.